Hello,
i want to generate fixed number of pulses using function generator,
it does not support burst mode,so while searching for it i found that using
gate trigger and applying external peiodic pulse we can have it...in on period of that pulse but i am not getting that we can not generate fixed number of pulses without using external signal??

Typically, the external gate circuitry causes the function generator to output its signal when the gate signal is a TTL logic high and inhibits the output when the gate signal is a TTL logic low.

One technique is to use a second function generator to supply the gate signal. The second function generator is set to a period that is half of the desired length of the output pulses. You have to be careful with triggering, as it's easy to get off-by-one errors in the burst count.

If you have access to a PIC chip and programmer, it's pretty easy to program one to give the exact burst you need.